Blast Initiation and Propagation of Cylindrical Detonations in MAPP-Air Mixtures

Abstract

An experimental investigation of the initiation, transition and quasi-steady propagation of blast initiated cylindrical detonations in Methyl Acetylene, Propane, Prodadiene (MAPP)-air mixtures is described. A sectored shock tube was employed which was originally designed to allow study of cylindrical shock, and homogeneous and heterogeneous detonation waves. Cylindrical blast waves were generated by firing of controlled amounts of a condensed explosive at the apex of the sector. Experimental data served to suggest the existence of three wave propagation regimes: subcritical energy regime, where decoupling of shock and reaction zone results in a reacting blast wave-type decay; the critical energy regime, where decoupling occurs but is followed by the re-establishment of a sub-Chapman-Jouguet condition, with an asymptotic strengthening to the C J state; and supercritical energy regime, where the initially overdriven detonation decays asymptotically to its CJ state. Threshold energy levels delineating the subcritical to critical energy regimes were established for a wide range of MAPP-air mixtures. Lean and rich limits for steady propagating detonation waves were also established. Comparisons made with the work of others reveal that these limits do not suffer from scale effects. The detonation velocity, when attained, displayed a definite dependence on blast wave energy with the higher energy runs giving reasonable agreement with theory. The measured transition distances from blast to detonation wave, nondimensionalized by the blast wave explosion length, compared satisfactorily with theoretical predictions.